The present invention generally relates to pilot signal recording and reproducing systems, and more particularly to a pilot signal recording and reproducing system which records four kinds of pilot signals for detecting tracking error information on a recording medium by changing over the pilot signal for every track turn, and capable of reproducing the pilot signals as signals having accurate tracking error information by use of a circuit having a simple circuit construction.
Recently, in magnetic recording and reproducing apparatuses for home use (hereinafter simply referred to as a home VTR) having helical scan type rotary heads, high density recording and reproduction are becoming possible due to improvements in the magnetic tape and the realization of high density rotary heads. Accordingly, home VTRs have been manufactured which are capable of performing long-duration recording and reproduction of six hours, for example, by reducing the tape speed, the track pitch, and the like, to approximately one-third of the values for the case where two hours of recording and reproduction is possible. However, since the tape driving system in the home VTR is simplified in order to reduce the cost of the apparatus, it becomes difficult to accurately and stably maintain a desired tracking accuracy by tracing over the bends of the video track, upon high density recording and reproduction. Especially upon a so-called interchanged reproduction in which a magnetic tape recorded by a home VTR is reproduced by another home VTR, it is difficult to stably maintain the above desired tracking accuracy, and a high quality picture could not be obtained.
Hence, as a method of solving the problems with respect to tracking introduced during the above high density recording and reproduction, and eliminating the noise bar introduced during a special reproduction mode such as a slow-motion reproduction mode, a still reproduction mode, and a quick-motion reproduction mode in which reproduction is performed with a tape travelling speed which is different from that upon recording, that is, to eliminate the noise bar introduced because the head scanning locus does not accurately coincide over the recorded track, a head moving mechanism is provided in the home VTRs which are recently being developed. This head moving mechanism displaces the rotary heads in a plane which is perpendicular with respect to the rotating plane of the rotary heads, and displaces the rotary heads in a direction perpendicular with respect to the track longitudinal direction, that is, along the width direction of the track.
In a home VTR provided with the above described head moving mechanism, the rotary heads accurately follows and traces over the bends in the track, and during the special reproduction mode in which the tape travelling speed is different from that upon recording, the head scanning locus accurately follows over the track. These operations are performed by detecting a relative error information (tracking error information) between the track which is to be reproduced and the rotary head which is actually tracing over the magnetic tape, and producing a tracking error signal according to the above tracking error information to correct the tracking error of the rotary head, by use of a tracking servo circuit. In this type of a home VTR, it is extremely important and essential to accurately detect the above tracking error information when correcting the tracking error.
Conventionally, as a method of detecting the above tracking error information, there was a system in which four kinds of pilot signals were recorded in a continuous manner for each track. These four kinds of pilot signals are changed over and recorded for every recording unit of one track, so that the frequency of the pilot signal is different between mutually adjacent tracks. Upon reproduction, the frequency of the reproduced pilot signal is discriminated, and the tracking error information is detected from the above reproduced level. However, a wide frequency band was required for a filter circuit provided in the reproducing system, which was used for selecting the respective frequencies of the four kinds of pilot signals.
On the other hand, another conventional system oscillated the rotary head in the width direction of the track with a sinusoidal wave in the order of 420 Hz or 480 Hz, so that the rotary head formed a scanning locus of a sinusoidal wave shape with respect to one recorded track. In this system, the tracking error was detected from a level difference between adjacent positive peak point and negative peak point in the above scanning locus of the sinusoidal wave shape of the reproduced FM level, of the information signal which is recorded on the track as a form of frequency modulated signal (FM signal). However, in this conventional system, since the detection is performed with respect to the difference between the reproduced FM signals at the above adjacent positive peak point and negative peak point, there was a disadvantage in that errors were introduced upon detection of the tracking error due to the fact that the detecting positions were different. Moreover, in the above described conventional system, when reproduction is performed with respect to a magnetic tape which is recorded with an azimuth recording system by use of rotary heads, these rotary heads are oscillated along the width direction of the track. Accordingly, a shift was introduced in the time axis during the reproduction of the signal, and there was a disadvantage in that instability was introduced in the color and distortion was introduced in the reproduced picture due to the above shift in the time axis. Furthermore, there was a further disadvantage in this system in that, the tracking error information could not be obtained accurately with respect to a tracking error exceeding one track pitch.